Air conditioning apparatus



March 9, 1965 c. F. ALSING 3,172,272

AIR CONDITIONING APPARATUS Original Filed Aug. 21, 1959 REVERS/NG VALVEFIGI.

OUTDOOR COIL N DOOR COIL CAPILLA RY TUBE \cAP/LLARY TJBE FIGZ.

WITNESS INVENTOR CARL F. ALSING ATTORNEY United States PatentOfiice3,172,272 Patented Mar. 9, V 1965 ,172,272 AER C(FNDETIUNING APPARATUSCarl F. Alsing, Springfield, Mass, assignor to Westinghouse ElectricCorporation, East Pittsburgh, Pa, a corporation of PennsylvaniaContinuation of abandoned application Ser. No. $35,295, Aug. 21, 1959.This application June 19, 1962, Ser. No. 205,177

4 Claims. (Cl. 62-624) This invention relates to air conditioningapparatus and more particularly to a reversible heat pump system in airconditioning apparatus used for either heating or cooling air forcomfort.

Conventional apparatus of the class set forth includes an indoor heatexchanger or coil which acts as an evaporator during the coolingoperation, and an outdoor heat exchanger or coil which, at the sametime, acts as a condenser. Conversely, during the heating operation thedirection of refrigerant flow is reversed and the indoor coil acts as acondenser while the outdoor coil acts as an evaporator.

A slender, restricted bore tube is connected between the indoor andoutdoor coils for the purpose of reducing the pressure, in eitherdirection of flow between these heat exchangers. The tube is commonlyknown in the re frigeration art as a capillary tube.

A fixed flow restrict-or that is a proper selection for thethermodynamic characteristics of the system during cooling operation isusually unsuitable for the systems efficient operation during heatingoperation. Unless the effective impedance of the capillary tube isgreater during heating, the undesirable condition in which liquidrefrigerant flows through to the compressor can result. This problem iswell recognized in the refrigeration art and various means have beenproposed previously to cope with it.

In dealing with this problem the present invention utilizes, in a uniquearrangement, the well-known principle that the effective impedance ofthe restricted bore tube is increased by the vaporization of liquidrefrigerant therein. in accordance with the invention, a portion of hecapillary tube near its end connected to the indoor coil is arranged inheat transfer relationship with the refrigerant in a portion of therefrigerating system adjacent said end of the capillary tube andcontaining, during heating operation, refrigerant condensed in theindoor coil. This relationship may be established, for example, byinserting the end portion of the capillary tube in the run of the indoorcol to which the capillary tube is connected. This arrangement, inaddition to providing increased elfective impedance to flow duringheating operation, to some extent adjusts or regulates the effectiveimpedance to maintain within certain limits the quantity of liquidrefrigerant present in the indoor coil.

The various objects, features and advantages of the invention willappear more fully from the detailed description which follows, taken inconnection with the accompanying drawing, forming a part hereof, inwhich:

FIG. 1 is a diagrammatic view of a reversible refrigerating systemembodying the invention; and

FIG. 2 is an enlarged sectional view of a fragmentary portion of FIG. 1,showing in detail the preferred arrangement of the capillary tube withinthe indoor coil.

The invention, as diagrammatically shown, is applied to a reversibleheat pump system including an indoor coil or heat exchanger 10 and anoutdoor coil or heat exchanger 12, both of which may be of theconventional cross-finned serpentine coil type. Although not shown,provision is made for conveying air over the coil 10 and delivering thesame to the enclosure to be air conditioned. The coil 10 serves as theevaporator during cooling operation and as the condenser during heatingoperation. The outdoor coil 12 is placed in heat transfer relationshipWith the outside atmosphere and, here too, provision is made forconveying outside air over the coil 12 and discharging the same tooutdoors or to some other place exterior of the enclosure. The coil 12serves as the condenser during cooling operation and as the evaporatorduring heating operation.

In the illustrated embodiment of this invention, the runs or tubes ofeach coil are disposed horizontally and connected to provide arefrigerant path extending from the top through the successively lower,adjacent runs to the bottom of the coil so that, when the coil isserving as the condenser, gravity assists the condensed refrigerant inflowing to the bottom or extreme lower region of the coil.

The system further includes a motor-compressor 14 having a suction line16 and a discharge line 18, both connected to a reversing valve 29. Thereversing valve 20 is adapted to place the compressor suction line 16and discharge line 18 in communication with the coils l0 and 12,respectively, for cooling the enclosure, and to reverse the connectionsand place them in communication with the coils 12 and 10, respectively,for heating the enclosure. Suitable provision is made for actuating thereversing valve 20, as by a manually movable knob 22.

A flow restrictor, which provides pressure reducing or expansion means,is connected between the indoor coil 15 and the outdoor coil 12.Preferably, the flow restrictor comprises a slender, restricted boretube 24, commonly referred to in the art as a capillary tube. In FIG. 1,the flow of refrigerant during the cooling cycle is indicated by solidline arrows, and broken line arrows indicate the flow during the heatingcycle.

In accordance with the present invention, the capillary tube 24 has aportion of its length, preferably an end portion near its connection tothe indoor coil it), placed in heat transfer relationship with a portionof the refrigerating system adjacent said end of the capillary tubeconnected to the indoor coil and containing, during heating operation,refrigerant condensed in the indoor coil. For example, said end portionof the capillary tube may be arranged in heat transfer relation with therun of the indoor coil 10 adjacent the connection (see FIG. 2). It is tobe understood that a heat transfer relationship between the mentionedportions of the coil 10 and the capillary tube 24 can be established byvarious arrangements, such as by soldering portions of their respectivetubes together; but, preferably, the end portion of the capillary tube24 is doubled back on itself in a hairpin shape and inserted in the runof the coil 1%), so that the end of the capillary tube is adjacent theconnection be tween the tube and the coil. Refrigerant in a liquid statetends'to collect at the end of its flow path in a condenser coil; and,by placing a length of the capillary tube 24 in intimate contacttherewith, the flow of refrigerant through tube 24 is affected bychanging refrigerant conditions within the indoor coil 10.

T [leery of operation The capillary tube conducts refrigerant from thecoil acting as condenser to the coil acting as evaporator. It alsoexpands refrigerant from condenser pressure to evaporator pressure; andthe pressures within these coils are largely affected by theirrespective environmental air temperatures. Based on the averageenvironmental air temperatures for which the refrigeration system isdesigned, as well as the compressor pumping rate (in lbs. per hour) andthe surface area of each coil, the required effective impedance of thecapillary tube is determined; and a suitable capillary tube whichprovides the required effective impedance is selected according to itslength and bore. It is the general practice to make this selection onthe basis of requirements for cooling operation of the circuit.

Although restricted bore tubes have been highly successful when used inrefrigeration systems of the nonreversible type, they have presentedspecial problems when employed in reversible refrigeration systems usedin air conditioning apparatus for both heating and cooling. Principallythe problem concerns thermodynamic efficiency, since an effectiveimpedance which is correct for the cooling operation and one directionof refrigerant flow is all too often wrong for the heating operationwhen the direction of flow is reversed. In back of this problem is thefact that the range of environmental air temperatures for the coils isconfined to a generally lower level for Winter operation than for summeroperation, and it follows that refrigerant on the suction side of thecompressor will be less dense and the compressor will pump refrigerantinto the condenser at a lower rate, weightwise, during winter operation.Also involved i the larger temperature difference between average indoorand outdoor temperatures during the winter time, which in turn, producesa larger pressure difference between the coils and across the capillarytube, which tends to increase the rate of refrigerant flow through thecapillary tube. These two consequences of winter operation, namely,reduced refrigerant flow to the condenser and increased refrigerant flowfrom the condenser, tend to reduce the accumulation of refrigerant inthe condenser. It follows that a capillary tube ideally suited for thecooling operation of the system may have an effective impedance so smallthat all liquid refrigerant will be emptied from the condenser and hotgas will flow from the condenser into the evaporator when the system isswitched over to heating operation. And this is obviously objectionable.Therefore, it is the concern of the present invention to provide anarrangement in which the capillary tube will have a greater effectiveimpedance during heating operation than during cooling operation.

Obviously, a capillary tube could be selected that would possess theproper impedance characteristics for heating operation but it wouldprovide too great an impedance during most conditions of coolingoperation. It may be mentioned in passing that a capillary tube shouldnot provide too great an impedance or else the evaporator will bestarved and the condenser will be flooded. In such a situation, bothcoils operate at reduced heat transfer efficiency, and the compressoralso operates at a lower efiiciency.

With the present invention, a portion of the capillary tube 24 isinserted within the indoor coil 10 where it is in heat transferrelationship with the refrigerant therein, which arrangement changes theeffective impedance of the tube. When the inserted portion of the tubeis cooled, heat is extracted from the refrigerant flowing therethroughand this negatives to some extent the flow impedance of this insertedtube portion by inhibiting further vaporization of the refrigerant andpromoting its condensation. Conversely, adding heat to the refrigerantflowing through the capillary tube promotes its vaporization and therebyincreases the effective impedance of the tube. Although this principleis well known in the refrigeration art and has been used in one way oranother in prior art reversible cycle systems, the present arrangementis unique in placing a portion of the capillary tube in heat transferrelationship with the portion of the indoor coil near the connectionbetween the indoor coil and the tube.

Cooling operation During cooling operation of the system condensedliquid refrigerant leaves the outdoor coil 12, which is act ing as acondenser, and enters the capillary tube 24 at substantially thedischarge pressure of the motor-compressor 14. While traveling throughthe uninserted length of capillary tube 24, which is surrounded by air,a small but progressively increasing portion of liquid refrigerantvaporizes as its pressure is progressively reduced. This progressivelyincreases the effective impedance of each unit length of the capillarytube as the refrigerant approaches the outlet end of the tube.

However, the impedance offered by that portion of the capillary tubewhich is bathed in cool refrigerant in the indoor coil 10 isconsiderably less than the impedance which this same portion of the tubewould offer if it were not so cooled because the lower temperature towhich it is subjected inhibits further vaporization of refrigerantflowing through the capillary tube. This enables the designer of thesystem to select for conditions of cooling operation a somewhat longeror more restricted capillary tube, which is then available to offeradditional impedance during heating operation.

Heating operation It will now be assumed that the system is operating atan ideal flow rate to heat an enclosure and the indoor coil 10 is actingas a condenser. Under such conditions, liquid refrigerant in thecondenser covers the inlet to the capillary tube 24, thus serving tokeep gaseous refrigerant from entering the capillary tube.

As liquid refrigerant flows through the capillary tube 24, expansion andcooling thereof takes place and additional heat is absorbed from thewarm liquid refrigerant in the indoor coil 10. The additional heatimparted to the refrigerant in the capillary tube causes thisrefrigerant to commence to vaporize sooner in its travel through thecapillary tube and increases the effective impedance of the capillarytube over what it would be were this portion of the capillary tube notso heated.

It can thus be seen that a capillary tube having an end portion thereofin heat transfer relationship with refrigerant at this one end of theindoor coil offers substantially greater impedance to refrigerant flowduring heating operation than during cooling operation. The impedance ofthe capillary tube is thereby more nearly matched to the flow rate ofrefrigerant through the other components of the system during heating toinsure that a liquid seal will always be maintained at the outlet of theindoor coil.

Regulating feature It is well understood in the refrigeration art thatthe condenser component of a refrigerating or heat pumping systemfunctions most efficiently when the level of liquid refrigerant thereinis at, or near, the outlet end of the condenser. If additional passes orruns of the condenser are permitted to become filled with liquidrefrigerant less surface area is available on which vaporous refrigerantcan be condensed. The heat exchange relationship between a portion ofthe capillary tube 24 and the refrigerant within one pass of the indoorcoil 10 provides for regulation of the amout of liquid refrigerant whichaccumulates in the indoor coil for a given range of operating conditionsto which the apparatus is subjected.

As mentioned previously, the effective impedance of the capillary tube24 is increased when the system is placed in heating operation so as toprevent all of the liquid refrigerant from leaving the indoor coil 14?.This increase of impedance is effected by the addition of heat torefrigerant flowing through the capillary tube. It can be readilyappreciated that as the liquid level in the indoor coil approaches theoutlet end of the last pass of the coil a greater length of thecapillary tube 24 is exposed to vaporous refrigerant in the coil. Thisresults in more heat being added to this inserted portion of thecapillary tube; first, because the heat of condensation is availablefrom the vaporous refrigerant and secondly, because the vaporousrefrigerant is warmer than the liquid refrigerant, which is subcooled tosome extent. Thus, as operating conditions change, for example, theoutdoor air temperature falls, and refrigerant begins to flow morerapidly through the capillary tube 24, the liquid level in the coil 10falls, exposing an increasing length of the capillary tube to warmvaporous refrigerant which, in turn, beats and increases the effectiveimpedance of the capillary tube. Eventually, a state of equilibrium isreached and the liquid level stabilizes at some point near the outlet ofthe indoor coil.

When conditions change so as to cause the liquid level to rise in theindoor coil 10, say, for example, the outdoor temperature rises rapidly,more of the inserted portion of the capillary 24 willbecome covered withliquid refrigerant. The quantity of heat available to be added to thisportion of the capillary tube becomes less as less vaporous refrigerantremains in contact with the capillary tube. Depending upon the degree ofchange of conditions, the liquid level will stabilize at a higher pointin the indoor coil 10 as the effective impedance of the capillary tube24 is reduced to match the flow conditions of the system.

In a properly designed system this movement of the liquid level can beconfined to that portion of the indoor coil which contains the insertedportion of the capillary tube 24, so that only this lower or last run ofthe indoor coil is likely to be flooded with liquid refrigerant, therebyleaving the remainder of the indoor coil available as condensing surfacearea.

Conclusion From the foregoing it will be apparent that arranging aportion of the capillary tube 24 in heat transfer rela tion withrefrigerant in the indoor coil 16) not only has the general effect ofincreasing the effective impedance of the tube during heating, but alsoaccomplishes regulation of the effective impedance of the capillary tubeduring heating operation in response to refrigerant conditions withinthe coil 10.

It will be appreciated that the ideal length and bore of a capillarytube, as well as the ideal amount thereof to be inserted, varies withthe capacity of the refrigeration system and expected ambientconditions. However, in one working model of a room air conditionerhaving a cooling capacity of approximately three-quarter ton andembodying the present invention, a capillary tube 36 inches long andhaving a bore .059 inch in diameter was effectively employed with 16inches of its length inserted in the indoor coil 10.

While the invention has been shown in but one form, it will be obviousto those skilled in the art that it is not so limited, but issusceptible of various changes and modifications without departing fromthe spirit thereof.

This application is a continuation of application Serial No. 835,205,filed August 21, 1959.

What is claimed is:

1. In a reversible system for heating and cooling air for an enclosure,

a compressor,

a first heat exchanger for conditioning enclosure air,

a second heat exchanger in heat transfer relationship with outdoor air,

6 means including a reversing valve for selectively connecting thedischarge and the suction of said compressor to said first and secondheat exchanger respectively during heating operation and to said secondand first heat exchangers respectively during cooling operation, and acapillary tube connected between said heat exchangers and serving toexpand refrigerant from condensing pressure to evaporating pressureduring both the heating and the cooling operations, said capillary tubebeing out of heat transfer relationship with the refrigerant flowingthrough said second or outdoor heat exchanger, said capillary tubehaving a portion thereof in heat transfer relationship with a portion ofthe refrigerating system adjacent the end of the capillary tubeconnected to the first heat exchanger and containing, during heatingoperation, refrigerant condensed in said first heat exchanger, wherebythe flow rate of refrigerant through the refrigerating system is lowerduring heating operation than during cooling operation. 2. In areversible system for heating and cooling air for an enclosure,

a compressor, a first heat exchanger for conditioning enclosure air, asecond heat exchanger in heat transfer relationship with outdoor air,-means including a reversing valve for selectively connecting thedischarge and the suction of said compressor to said first and secondheat exchangers respectively during heating operation and to said secondand first heat exchangers respectively during cooling operation, and acapillary tube connected between said heat exchangers and serving toexpand refrigerant from condensing pressure to evaporating pressureduring both the heating and the cooling operations, said capillary tubebeing out of heat transfer relationship with the refrigerant flowingthrough said second or outdoor heat exchanger, said capillary tube andsaid first heat exchanger having portions thereof near the connectiontherebetween arranged in heat transfer relationship for regulating theflow rate of refrigerant through said refrigerating system. 3. In areversible system for heating and cooling air for an enclosure,

a compressor, a first heat exchanger for conditioning enclosure air, asecond heat exchanger in heat transfer relationship with outdoor air,means including a reversing valve for selectively connecting thedischarge and the suction of said compressor to said first and secondheat exchangers respectively during heating operation and to said secondand first heat exchangers respectively during cooling operation, and acapillary tube connected between said heat exchangers and serving toexpand refrigerant from condensing pressure to evaporating pressureduring both the heating and the cooling operation, said capillary tubebeing out of heat transfer relationship with the refrigerant flowingthrough said second or outdoor heat exchanger and having a substantialportion thereof adjacent the connection to said first heat exchangerinserted in a portion of said first heat exchanger so that a heattransfer relationship is established between said capillary tube portionand the refrigerant in said first heat exchanger portion, whereby therate of refrigerant flowing through said capillary tube is regulated. 4.In a reversible system for heating and cooling air for an enclosure,

a compressor, a first heat exchanger for conditioning enclosure air,

a second heat exchanger in heat transfer relationship with outdoor air,

means including a reversing valve for selectively connecting thedischarge and the suction of said compressor to said first and secondheat exchangers respectively during heating operation and to said secondand first heat exchangers during cooling operation, and

a capillary tube connected between said heat exchangers and serving toexpand refrigerant from condensing 10 pressure to evaporating pressureduring both the heating and the cooling operation; said capillary tubebeing out of heat transfer relationship with the refrigerant flowingthrough said second or outdoor heat exchanger and having one endconnected to said second heat exchanger, and another end including asubstantial length of tube adjacent thereto inserted in said first heatexchanger, whereby a heat transfer relationship for regulating the flowrate of refrigerant through said refrigerating system is establishedbetween the refrigerant in the inserted length of said capillary tubeand the refrigerant in said first heat exchanger.

Coyne June 19, 1956 Stevens Oct. 18, 1960

1. IN A REVERSIBLE SYSTEM FOR HEATING AND COOLING AIR LOR AN ENCLOSURE,A COMPRESSOR, A FIRST HEAT EXCHANGER FOR CONDITIONING ENCLOSURE AIR, ASECOND HEAT EXCHANGER IN HEAT TRANSFER RELATIONSHIP WITH OUTDOOR AIR,MEANS INCLUDING A REVERSING VALVE FOR SELECTIVELY CONNECTING THEDISCHARGE AND THE SUCTION OF SAID COMPRESSOR TO SAID FIRST AND SECONDHEAT EXCHANGERS, RESPECTIVELY DURING HEATING EXCHANGERS RESPECTIVELYDURING OND AND FIRST HEAT EXCHANGERS RESPECTIVELY DURING COOLINGOPERATION, AND A CAPILLARY TUBE CONNECTED BETWEEN SAID HEAT EXCHANGERSAND SERVING TO EXPAND REFRIGERANT FROM CONDENSING PRESSURE TOEVAPORATING PRESSURE DURING BOTH THE HEATING AND THE COOLING OPERATIONS,SAID CAPILLARY TUBE BEING OUT OF HEAT TRANSFER RELATIONSHIP WITHREGRIGERANT FLOWING THROUGH SAID SECOND OR OUTDOOR HEAT EXCHANGER, SAIDCAPILLARY TUBE HAVING A PORTION THEREOF IN HEAT TRANSFER RELATIONSHIPWITH A PORTION OF THE REFRIGERATING SYSTEM ADJACENT THE END OF THECAPILLARY TUBE CONNECTED TO THE FIRST HEAT EXCHANGER AND CONTAINING,DURING HEATING OPERATION, REFRIGERANT CONDENSED IN SAID FIRST HEATEXCHANGER, WHEREBY THE FLOW RATE OF REFRIGERANT THROUGH THEREFRIGERANTING SYSTEM IS LOWER DURING HEATING OPERATION THAN DURINGCOOLING OPERATION.